GTA Online, Off topic Question!

Mr-Infinite_Rage

Hello, last night me, my brother, and my friend, were playing GTA Online, and we were in a private Party "Locked" as always I was the host, I always lock my parties, and someone random joined our party I heard this person talking then this person left, this person is on neither of our friends list. How did this person join an invite only party? I can't remember what this person said, it was a guy! This is the first time it's happened!